Move self_less to the is_less callable #2550

Job	Run time
no_pch (clang, x86, -msse2)	1m 50s
nosimd (clang, x86, -DEVE_NO_SIMD)	3m 3s
riscv (clang, riscv, -mrvv-vector-bits=128)	3m 4s
no_pch (gcc, x86, -msse2)	2m 2s
externals (clang, x86, -msse2)	1m 10s
nosimd (gcc, x86, -DEVE_NO_SIMD)	3m 3s
externals (gcc, x86, -msse2)	53s
arm (clang, aarch64, -Wno-psabi)	1s
macosx (clang, x86_osx, -mavx)	1m 0s
x86-clang (clang, x86, -msse4.2)	1s
arm (clang, arm, -Wno-psabi)	1s
x86-clang (clang, x86, -mavx)	1s
x86-clang (clang, x86, -mavx2)	3m 7s
avx512	1s
other-cases	1s
other-arch	1s
x86-gcc	1s
	19m 20s

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